eBPF Debugging

Debugging Performance Bottlenecks with eBPF¶

eBPF's ability to trace kernel functions and measure execution times makes it invaluable for diagnosing performance issues. It can isolate bottlenecks in I/O, CPU, or network operations using eBPF-specific tools like BCC or bpftrace.

Example: Profiling System Calls with bpftrace¶

To measure the time spent in system calls:

bpftrace -e 'tracepoint:syscalls:sys_enter_* { @start = nsecs; } tracepoint:syscalls:sys_exit_* { @duration = nsecs - @start; }'

This logs the duration of each system call, helping identify slow or frequent calls through aggregated metrics.

Example: Tracing Kernel Functions with BCC¶

Using BCC's perf tool (note: B.CC's perf is eBPF-based, distinct from the standalone perf utility):

sudo bcc/perf -e 'syscalls:sys_enter_read' -a

This provides detailed profiling of system call execution, highlighting latency and frequency.

Advanced: Custom eBPF Programs¶

For deeper insights, write custom programs to trace specific kernel functions (e.g., vfs_read for I/O bottlenecks) and aggregate metrics using tools like bcc or libbpf.

Detecting Memory Leaks with eBPF¶

eBPF enables precise tracking of memory allocations and deallocations to detect kernel leaks. Tools like BCC and custom eBPF programs can monitor kmalloc and kfree events to identify unclaimed memory.

Example: Tracking kmalloc with BCC¶

Use BCC's kfree tool to monitor memory deallocations:

sudo bcc/kfree -p

This logs freed memory addresses and sizes, helping identify allocations that are never freed. For deeper analysis, combine kmalloc and kfree probes to track allocation lifetimes.

Example: Custom eBPF Program for kmalloc¶

A custom eBPF program can log kmalloc events:

#include <vmlinux.h>
#include <bpf/trace.h>

struct alloc_info {
    __u64 addr;
    __u64 size;
};

struct {
    __uint(type, BPF_MAP_TYPE_HASH);
    __uint(max_entries, 1024);
    __type(key, __u64);
    __type(value, struct alloc_info);
} alloc_map SEC(".maps");

int trace_kmalloc(struct pt_regs *ctx, void *ptr, size_t size) {
    struct alloc_info info = {.addr = (unsigned long)ptr, .size = size};
    bpf_map_update_elem(&alloc_map, &info.addr, &info, BPF_ANY);
    return 0;
}

This program records memory allocations and can be paired with kfree probes to detect leaks by checking if entries persist after deallocation.

Key takeaways¶

eBPF enables low-overhead monitoring of kernel and process behavior, ideal for security and debugging.
Memory leak detection can be achieved with BCC tools like kfree or custom eBPF programs tracking kmalloc/kfree events.
Process tracking via system calls and file access helps identify security risks or misbehavior.
Performance profiling using eBPF and BCC tools isolates bottlenecks in system calls, I/O, or network operations.
Always consider kernel version compatibility and performance trade-offs when deploying eBPF programs.